Drive motor for use in variable valve operating device for internal combustion engine

ABSTRACT

An actuator of a variable valve operating device includes an electric motor for varying the distance by which an intake valve of an internal combustion engine is lifted. The electric motor has a hollow cylindrical magnet assembly disposed around a hollow cylindrical holder, and a shaft rotatably supported in a housing, with a hollow region being defined between the shaft and the holder. The magnet assembly is skew-magnetized at a predetermined angle to the axis of the magnet assembly.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a drive motor for use in a variable valve operating device in an internal combustion engine for controlling the angular displacement of a control shaft angularly movably supported in the cylinder head of the internal combustion engine thereby to control the distance by which a valve is lifted in response to the displacement of a cam shaft.

2. Description of the Related Art

As disclosed in Japanese Laid-Open Patent Publication No. 2006-307713, for example, there is known a variable valve operating device including a drive motor for angularly moving a cam shaft that is angularly movably supported in the cylinder head of an internal combustion engine. In recent years, drive motors for use in variable valve operating devices for internal combustion engines have been required to be more responsive and smaller in size.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide a drive motor for use in a variable valve operating device in an internal combustion engine, which drive motor is more responsive when energized, can smoothly be operated, and is small in size.

The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevational view, partly omitted from illustration, of an internal combustion engine incorporating a variable valve operating device which includes a drive motor according to an embodiment of the present invention;

FIG. 2 is an enlarged side elevational view of a lift varying mechanism and nearby parts of the variable valve operating device shown in FIG. 1;

FIG. 3 is an exploded perspective view of the lift varying mechanism shown in FIG. 2;

FIG. 4 is a vertical cross-sectional view of an actuator of the variable valve operating device shown in FIG. 1;

FIG. 5 is an enlarged cross-sectional view of an electric motor and nearby parts of the actuator shown in FIG. 4;

FIG. 6 is a perspective view of a rotor of the electric motor of the actuator shown in FIG. 4;

FIG. 7 is an exploded perspective view of the rotor shown in FIG. 6; and

FIG. 8 is a side elevational view of the rotor shown in FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1, a variable valve operating device 10 which includes a drive motor according to an embodiment of the present invention is incorporated in an internal combustion engine.

As shown in FIGS. 1 through 3, the variable valve operating device 10 is mounted in a cylinder head 14 fixedly mounted on a cylinder block 12 of the internal combustion engine which has a plurality of cylinders. The cylinder head 14 houses therein an intake valve 16 openably and closably disposed in an intake port of each of the cylinders. The intake valve 16 is opened and closed by the variable valve operating device 10.

For each of the cylinders, the variable valve operating device 10 comprises a camshaft 20 having a valve operating cam 18, a rocker arm 22 swingably displaceable in response to movement of the valve operating cam 18 for operating the intake valve 16, and a lift varying mechanism 24 for continuously varying the distance by which the intake valve 16 is lifted to open the intake port. The variable valve operating device 10 further comprises an actuator 26 for actuating the lift varying mechanism 24.

As shown in FIG. 2, an upper holder 28 a is fastened to the cylinder head 14 and disposed on both sides of the cylinders. The camshaft 20 is rotatably supported by a cap 30 mounted on an upper surface of the upper holder 28 a.

The rocker arm 22 is of a substantially V-shaped cross section bent through a predetermined angle. A tappet screw 34 held in abutment with a stem 32 of the intake valve 16 is axially adjustably threaded through an end of the rocker arm 22. A roller 40 is rotatably supported by a substantially central portion of the rocker arm 22 through a first coupling shaft 36 and a needle bearing 38. The roller 40 is held in rolling abutment against the outer circumferential surface of the valve operating cam 18 on the camshaft 20.

As shown in FIGS. 2 and 3, the lift varying mechanism 24 includes a first link arm 44 having an end angularly movably coupled to the substantially central portion of the rocker arm 22 and another end angularly movably supported by a fixed shaft 42. The lift varying mechanism 24 also includes a second link arm 46 having an end angularly movably coupled to another end of the rocker arm 22 and another end angularly movably supported by a movable shaft 45. The lift varying mechanism 24 further includes a control shaft 48 engaged by the movable shaft 45 and angularly displaceable through a predetermined angle about the axis of the movable shaft 45.

The end of the first link arm 44 is of a substantially U-shaped cross section sandwiching the substantially central portion of the rocker arm 22 at its opposite sides, and is angularly movably supported by the first coupling shaft 36 by which the roller 40 is rotatably supported on the substantially central portion of the rocker arm 22. The fixed shaft 42 by which the other end of the first link arm 44 is angularly movably supported is supported by the upper holder 28 a.

The second link arm 46 is disposed below the first link arm 44. The end of the second link arm 46 is sandwiched by the other end of the rocker arm 22, and is angularly movably supported on the rocker arm 22 by a second coupling shaft 50 which extends through the other end of the rocker arm 22.

The control shaft 48 comprises a pair of webs 52 disposed one on each side of the rocker arm 22, a shaft 54 extending perpendicularly to the webs 52 and interconnecting pairs of webs 52, and a joint 56 interconnecting the webs 52. The movable shaft 45, which is disposed substantially parallel to the shaft 54, extends through the control shaft 48 across the webs 52 and is held thereby.

The shaft 54 of the control shaft 48 is angularly movably supported by the upper holder 28 a and a lower holder 28 b which is fastened to a lower surface of the upper holder 28 a (see FIG. 2).

When the intake valve 16 is placed in a closed state, the second coupling shaft 50 which connects the second link arm 46 to the rocker arm 22 is coaxial with the shaft 54 of the control shaft 48. When the control shaft 48 is angularly displaced about the shaft 54, the movable shaft 45 held by the control shaft 48 moves along an arcuate path about the axis of the shaft 54.

Specifically, when the control shaft 48 is angularly displaced to lower the movable shaft 45, and the roller 40 is pressed by the valve operating cam 18 of the camshaft 20, a four-link mechanism interconnecting the fixed shaft 42, the first coupling shaft 36, the second coupling shaft 50, and the movable shaft 45 is deformed to angularly displace the rocker arm 22 downwardly. The tappet screw 34 mounted on the end of the rocker arm 22 presses the stem 32 of the intake valve 16, lifting the intake valve 16 by a small distance to open the intake port.

When the control shaft 48 is angularly displaced to elevate the movable shaft 45, and the roller 40 is pressed by the valve operating cam 18 of the camshaft 20, the four-link mechanism is deformed to angularly displace the rocker arm 22 downwardly. The tappet screw 34 presses the stem 32 of the intake valve 16, lifting the intake valve 16 by a large distance to open the intake port.

The shaft 54 has an end portion projecting as a slightly long coupling shaft 58 laterally of the cylinder head 14. The coupling shaft 58 is inserted into a casing 60 (see FIG. 4) of the actuator 26 which is mounted on a side wall of the cylinder head 14.

As shown in FIG. 4, the actuator 26 comprises the casing 60, an electric motor 62 disposed in the casing 60 and having a drive shaft rotatable when the electric motor 62 is energized, a drive power transmitting mechanism 64 for transmitting drive power from the electric motor 62 to the control shaft 48, and a default mechanism 66 for holding the control shaft 48 in a predetermined angular position when the electric motor 62 is de-energized.

A first cover 68 is mounted on a side wall of the casing 60 by a plurality of bolts 70 in covering relation to the drive power transmitting mechanism 64. The casing 60 and the first cover 68 define a speed reducer mechanism housing chamber 72 therebetween. The speed reducer mechanism housing chamber 72 houses therein a speed reducer mechanism 74 of the drive power transmitting mechanism 64.

A second cover 76 is mounted on an opposite side wall of the casing 60 in covering relation to the default mechanism 66. The casing 60 and the second cover 76 define a default mechanism housing chamber 78 therebetween. The default mechanism housing chamber 78 houses therein the default mechanism 66.

As shown in FIGS. 4 and 5, the electric motor 62 is disposed in a motor housing hole 80 defined in a lower portion of the casing 60. The electric motor 62 comprises a housing 82, a rotor 84 rotatably held in the housing 82, and a stator 88 disposed around the rotor 84 and including a wound coil 86.

The rotor 84 comprises a shaft 90 rotatably supported in the housing 82, a hollow cylindrical holder 92 disposed around the shaft 90, and a magnet assembly 94 disposed around the holder 92.

The shaft 90 has both ends supported respectively by bearings 96 a, 96 b. A drive gear 98 is mounted on an end of the shaft 90 which is closer to the drive power transmitting mechanism 64. The drive gear 98 is held in mesh with a driven gear 100 of the drive power transmitting mechanism 64. A disk plate 102 is coupled to the other end of the shaft 90 which is closer to the default mechanism 66. The shaft 90 includes a slender shaft portion 104 having a radially inwardly reduced diameter in a substantially axially central position. The shaft 90 also includes a flange 106 having radially outwardly increased diameter between the slender shaft portion 104 and the end of the shaft 90 which is supported by the bearing 96 a.

The holder 92 comprises a large-diameter portion 108 disposed coaxially with the shaft 90 in covering relation to the slender shaft portion 104 of the shaft 90 and having a substantially constant diameter, and a small-diameter portion 110 disposed on an end of the large-diameter portion 108 and smaller in diameter than the large-diameter portion 108.

The large-diameter portion 108 extends up to the flange 106 in covering relation to the slender shaft portion 104 and a portion of the shaft 90 near the end of the shaft 90 which is supported by the bearing 96 a. The large-diameter portion 108 has an end held against the flange 106 to limit axial displacement of the shaft 90. The holder 92 is thus positioned with respect to the shaft 90.

The small-diameter portion 110 is disposed near the other end of the shaft 90 and holds an outer circumferential surface of the shaft 90. The small-diameter portion 110 is fitted over and held on the shaft 90, e.g., the small-diameter portion 110 is lightly press-fitted over the other end of the shaft 90.

An annular hollow region 112 having a given radial clearance is defined between the large-diameter portion 108 and the slender shaft portion 104. The annular hollow region 112 is held in fluid communication with the exterior of the holder 92 through a breather hole 114 defined in the junction between the large-diameter portion 108 and the small-diameter portion 110. Stated otherwise, the annular hollow region 112 is defined as a cylindrical space between the inner circumferential surface of the holder 92 and the outer circumferential surface of the slender shaft portion 104.

A flange 116 which projects slightly radially outwardly is disposed on the end, near the small-diameter portion 110, of an outer circumferential surface of the large-diameter portion 108. The flange 116 serves to position the magnet assembly 94 disposed around the holder 92.

The magnet assembly 94 comprises an Nd—Fe—B bonded magnet formed by mixing a powder of neodymium magnet with a plastic material and compression-molding or injection-molding the mixture, or an Nd—Fe—B sintered magnet formed by compression-molding a powder of neodymium magnet in a magnetic field and sintering the molded body. The magnet assembly 94 is in the form of a hollow cylinder whose diameter remains substantially constant in the axial direction. The magnet assembly 94 has an inside diameter which is substantially the same as the outside diameter of the large-diameter portion 108 of the holder 92 (see FIG. 5).

As shown in FIGS. 6 through 8, the magnet assembly 94 comprises a pair of coaxial magnets 94 a, 94 b, which have substantially the same axial lengths, arrayed along the axial direction of the holder 92. The magnets 94 a, 94 b are placed axially onto the large-diameter portion 108, and then secured to the holder 92. Specifically, the magnets 94 a, 94 b are bonded to the holder 92 by an adhesive applied to either the inner circumferential surfaces of the magnets 94 a, 94 b or the outer circumferential surface of the holder 92, so that the magnets 94 a, 94 b and the holder 92 are integrally combined with each other.

The magnet assembly 94 has an axial length which is essentially the same as the axial length of the large-diameter portion 108. Therefore, the magnet assembly 94 is mounted on the large-diameter portion 108 in covering relation to substantially the entire outer circumferential surface of the large-diameter portion 108.

The magnet assembly 94 is skew-magnetized, i.e., has skewed magnetic poles, at a given angle θ to the axis D of the magnets 94 a, 94 b (see FIG. 8). The magnetizing angle θ is optimally set to 15°, for example, with respect to the axis D of the magnets 94 a, 94 b.

The magnet assembly 94 is not limited to being made up of the magnets 94 a, 94 b, but may be of a three-piece structure made of three magnets having substantially the same shape disposed around the holder 92 or a one-piece structure made up of a single magnet disposed around the holder 92.

The drive power transmitting mechanism 64 is disposed between the coupling shaft 58 of the control shaft 48 and the electric motor 62. The drive power transmitting mechanism 64 transmits drive power from the electric motor 62 to the lift varying mechanism 24 including the control shaft 48.

The drive power transmitting mechanism 64 comprises a worm wheel 118 fixed to the coupling shaft 58, a worm gear 120 held in mesh with the worm wheel 118, and the speed reducer mechanism 74 disposed between the worm gear 120 and the electric motor 62.

The worm gear 120 is housed in a worm gear housing chamber 122 defined in the casing 60 above the motor housing hole 80. The worm gear 120 is disposed coaxially on a worm gear shaft 144 which has an end rotatably supported in the casing 60 by a ball bearing 124 and another end rotatably supported in the casing 60 by a needle bearing 126.

The end of the worm gear shaft 144 which is rotatably supported by the ball bearing 124 extends into the speed reducer mechanism housing chamber 72 housing therein the speed reducer mechanism 74. The speed reducer mechanism 74 includes a driven gear 100 mounted on the end of the worm gear shaft 144. The other end of the worm gear shaft 144 which is rotatably supported by the needle bearing 126 supports thereon a small-diameter gear 130 held in mesh with a large-diameter gear 128 of the default mechanism 66.

A worm wheel housing chamber 132 connected to the worm gear housing chamber 122 is provided at the upper of the casing 60. The worm wheel housing chamber 132 houses therein the worm wheel 118. The coupling shaft 58 has an end inserted into the worm wheel housing chamber 132, and the worm wheel 118 is coaxially fixed to the inserted end of the coupling shaft 58 by a bolt 70.

The speed reducer mechanism 74 comprises the drive gear 98 mounted on the end of the shaft 90 and the driven gear 100 held in mesh with the drive gear 98. The speed reducer mechanism 74 is housed in the speed reducer mechanism housing chamber 72 that is defined between the casing 60 and the first cover 68. The speed reducer mechanism 74 reduces the speed of drive power from the electric motor 62 at a ratio depending on the drive gear 98 and the driven gear 100, and transmits the reduced-speed drive power to the worm gear 120.

The default mechanism 66, which is housed in a default mechanism housing chamber 78 formed in the casing 60, comprises a default shaft 134 rotatably supported in the casing 60, the large-diameter gear 128 mounted on the default shaft 134 and held in mesh with the small-diameter gear 130 of the drive power transmitting mechanism 64, and a spring holder 136 disposed coaxially with the large-diameter gear 128.

The default mechanism 66 also comprises a first default spring 138 for normally urging the large-diameter gear 128 to move in a direction to abut against the spring holder 136, and second and third default springs 140, 142 for normally urging the spring holder 136 to move in a direction opposite to the direction in which the first default spring 138 normally urges the large-diameter gear 128, while the large-diameter gear 128 and the spring holder 136 are being held in abutment against each other.

The default shaft 134 is disposed substantially parallel to the worm gear shaft 144 and has both ends supported respectively by the casing 60 and the second cover 76. The large-diameter gear 128 is mounted on one of the ends of the default shaft 134, and held in mesh with the small-diameter gear 130 on the other end of the worm gear shaft 144. Therefore, the large-diameter gear 128 is operatively connected to the electric motor 62 through the small-diameter gear 130, the worm gear shaft 144, and the speed reducer mechanism 74.

The spring holder 136 is supported on the other end of the default shaft 134 and positioned adjacent to the large-diameter gear 128. The spring holder 136 is rotatable relatively to the large-diameter gear 128.

Engaging pins 146 project respectively from confronting end faces of the spring holder 136 and the large-diameter gear 128. The engaging pins 146 abut against each other upon angular movement of the large-diameter gear 128. When the large-diameter gear 128 is angularly moved to change the distance by which the intake valve 16 is lifted between a predetermined lifted distance and a minimum lifted distance, the spring holder 136 is angularly moved in unison with the large-diameter gear 128 about the default shaft 134 by the abutting engagement between the engaging pins 146.

The second and third default springs 140, 142 comprise helical springs, respectively, disposed around the spring holder 136. Each of the second and third default springs 140, 142 has an end engaging the spring holder 136 and another end engaging the casing 60.

Specifically, the second default spring 140 is disposed radially inwardly closely to the radially inner portion of the spring holder 136. The third default spring 142 is disposed radially outwardly in spaced relationship to the second default spring 140. The second and third default springs 140, 142 normally urge the spring holder 136 to move in the same direction from a minimum lifted distance position toward a predetermined lifted distance position.

As shown in FIG. 3, a tubular spring holder 148 is fixedly mounted on the coupling shaft 58 in surrounding relation thereto. The first default spring 138 is disposed around the spring holder 148. The first default spring 138 has an end engaging the cylinder head 14 and another end engaging the spring holder 148.

The variable valve operating device 10 incorporating the drive motor according to the present embodiment is basically constructed as described above. Operation and advantages of the variable valve operating device 10 will be described below.

When the electric motor 62 of the actuator 26 is de-energized, the worm gear 120 is angularly moved under the resiliency of the second and third default springs 140, 142, turning the worm wheel 118 through a predetermined angle. The control shaft 48 of the lift varying mechanism 24 which is coupled to the worm wheel 118 is turned to cause the movable shaft 45 to be angularly displaced to change the relative positions of the first and second link arms 44, 46, thereby angularly displacing the rocker arm 22 upwardly. As a result, the intake valve 16 pressed by the tappet screw 34 on the end of the rocker arm 22 is lifted by the predetermined lift distance to open the inlet port.

According to the present embodiment, the magnet assembly 94 of the electric motor 62 is in the form of a hollow cylinder, and is fitted over and secured to the holder 92 of the rotor 84. Even when the rotor 84 is rotated at a high speed upon energization of the electric motor 62, the magnet assembly 94 is prevented from being spaced radially outwardly from the holder 92. The magnet assembly 94 is therefore rotated in unison with the shaft 90 and the holder 92 at all times.

The magnet assembly 94 which comprises an Nd—Fe—B magnet is capable of producing greater magnetic forces than if the magnet assembly 94 comprises a ferrite magnet. In other words, if the magnet assembly 94 is to produce the same magnetic forces as a ferrite magnet, then the magnet assembly 94 may be smaller in size than the ferrite magnet.

If the magnet assembly 94 is reduced in size, then the rotor 84 including the magnet assembly 94 is reduced in weight. The moment of inertia of the rotor 84 is thus reduced, allowing the electric motor 62 to have an improved response, to reduce its power consumption, and to permit the rotor 84 to rotate more smoothly.

The magnet assembly 94 which comprises an Nd—Fe—B magnet tends to increase the cogging torque when the electric motor 62 is de-energized. However, since the magnet assembly 94 is skew-magnetized, as described above, the cogging torque is reduced, and the electric motor 62 including the magnet assembly 94 is reduced in size.

Inasmuch as the shaft 90 includes the slender shaft portion 104 with the hollow region 112 defined between the slender shaft portion 104 and the inner circumferential surface of the holder 92, the rotor 84 including the shaft 90 and the holder 92 is reduced in weight. Accordingly, the moment of inertia of the rotor 84 can be reduced. As a result, the electric motor 62 has an improved response and allows the rotor 84 to rotate more smoothly.

Since the hollow region 112 is defined between the slender shaft portion 104 and the holder 92, the weight of the rotor 84 is reduced in weight efficiently due to absence of materials between the holder 92 and the shaft 90.

Although a certain preferred embodiment of the present invention has been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims. 

1. A drive motor for use in a variable valve operating device disposed in a cylinder head of an internal combustion engine for controlling an angular displacement of a camshaft which is angularly movably supported in the cylinder head, comprising: a housing; a rotor including a shaft rotatably supported in said housing and a hollow cylindrical magnet assembly disposed around said shaft; and a stator disposed around said rotor and including a wound coil; said magnet assembly comprising a Nd—Fe—B magnet.
 2. A drive motor according to claim 1, wherein said magnet assembly has skewed magnetic poles.
 3. A drive motor according to claim 2, wherein said rotor has a hollow region defined between said magnet assembly and said shaft.
 4. A drive motor according to claim 3, wherein said hollow region is defined between a holder disposed around said shaft and holding said magnet assembly and a slender shaft portion of said shaft which faces said holder.
 5. A drive motor according to claim 4, wherein said holder has a breather hole through which said hollow region is held in fluid communication with the exterior of said holder.
 6. A drive motor according to claim 2, wherein said magnet assembly comprises a pair of magnets held by said holder, said magnets being arrayed along an axial direction of said holder.
 7. A drive motor according to claim 6, wherein said magnets are skew-magnetized at a predetermined angle to an axis of the magnets.
 8. A drive motor according to claim 7, wherein said predetermined angle is 15°. 